Various electro-optical systems have been developed for reading optical indicia, such as bar codes. A bar code is a coded pattern of graphical indicia comprised of a series of bars and spaces of varying widths, the bars and spaces having differing light reflecting characteristics. Some of the more popular bar code symbologies include: Uniform Product Code (UPC), typically used in retail stores sales; Code 39, primarily used in inventory tracking; and Postnet, which is used for encoding zip codes for U.S. mail. Systems that read and decode bar codes employing charged coupled device (CCD) or complementary metal oxide semiconductor (CMOS) based imaging systems are typically referred to hereinafter as imagining systems, imaging readers, imaging reader systems or bar code scanners.
Imaging reader systems electro-optically transform the graphic indicia into electrical signals, which are decoded into alphanumerical characters that are intended to be descriptive of the article or some characteristic thereof. The characters are then typically represented in digital form and utilized as an input to a data processing system for various end-user applications such as point-of-sale processing, inventory control and the like. Scanning systems of this nature have been disclosed for example, in U.S. Pat. Nos.: 4,251,798; 4,369,361; 4,387,297; 4,409,470; 4,760,248; and 4,896,026, all of which have been assigned to the assignee as the instant application.
Imaging readers employing CCD type technology typically use an illumination system to flood a target object with illumination from a light source such as a light emitting diode (LED) in the reader, and each CCD cell is sequentially read-out to determine the individual spacing in the bar code. Imaging systems include CCD arrays, CMOS arrays, or other imaging pixel arrays having a plurality of photosensitive elements or pixels. Light from the light source or LED is reflected from a target object, such as a bar code. The reflected light is then focused through a lens of the imaging system onto the pixel array, the target object being within a field of view of the lens. An analog-to-digital converter then digitizes output signals generated from the pixels of the pixel array. Decoding circuitry of the imaging system then processes the digitized signals and attempts to decode the imaged bar code.
Imaging readers are increasingly replacing laser type scanners that were utilize for many different applications. This is a result of the imaging readers' ability to offer more features than laser scanners, such as reading two-dimensional bar codes and capturing images such as checks and identification documents. A two-dimensional imaging reader is characterized by a photosensor array having multiple rows and multiple columns, that is an M×N array of M rows and N columns of photosensors or pixels. However, when processing one-dimensional bar codes, a laser scanner can often outperform an imager, especially a high-resolution imager. This is because of the additional time required for the imager to capture and process or search the entire image. In addition, the recent introduction of a megapixel sensor more than doubles the image resolution of earlier readers increasing from a 659×494 image to a now 1280×1024 image size, which as a result, increases the capture and process time. The evolution of the large pixel imaging results in longer time durations for image decoding because of the time needed to find the target object or bar code located within the captured image. Further processing time is wasted in existing imaging readers that focus a search in the outer extremes of the captured image, since it is less likely that the outer extremes would contain the intended target.
What is needed is a faster and more efficient approach to finding and decoding a target object or bar code.